Compilers4.1 Basic Macro Processor Functions 4.1.1 Macro Definition and Expansion
Fig. 4.1 shows an example of a SIC/XE program using macro instructions.
RDBUFF and WRBUFF
MACRO and MEND
RDBUFF is name
Parameters () of the macro instruction, each parameter begins with the character &.
Macro invocation () statement and the arguments () to be used in expanding the macro.
Fig. 4.2 shows the output that would be generated.
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. STRG
. STRG
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{ {
4.1.2 Macro Processor Algorithm and Data Structures
Two-pass macro processor All macro definitions are processed during the first pass.
All macro invocation statements are expanded during the second pass.
Two-pass macro processor would not allow the body of one macro instruction to contain definitions of other macros.
Such definitions of macros by other macros Fig. 4.3
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4.1.2 Macro Processor Algorithm and Data Structures
A one-pass macro processor that can alternate between macro definition and macro expansion.
The definition of a macro must appear in the source program before any statements that invoke that macro.
Inconvenience of the programmer.
Comment lines are not entered the DEFTAB.
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4.1.2 Macro Processor Algorithm and Data Structures
The macro names are entered into NAMTAB, NAMTAB contains two pointers to the beginning and the end of the definition in DEFTAB
The third data structure is an argument table ARGTAB, which is used during the expansion of macro invocations.
The arguments are stored in ARGTAB according to their position in the argument list.
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4.1.2 Macro Processor Algorithm and Data Structures
Fig. 4.4 shows positions of the contents of these tables during the processing.
Parameter &INDEV -> Argument ?1
Parameter &BUFADR -> Argument ?2
When the ?n notation is recognized in a line form DEFTAB, a simple indexing operation supplies the proper argument form ARGTAB.
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The macro processor algorithm itself is presented in Fig. 4.5.
The procedure PROCESSING
The procedure DEFINE Called when the beginning of a macro definition is recognized, makes the appropriate entries in DEFTAB and NAMTAB.
The procedure EXPAND Called to set up the argument values in ARGTAB and expand a macro invocation statement.
The procedure GETLINE Called at several points in the algorithm, gets the next line to be processed.
EXPANDING is set to TRUE or FALSE.
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4.1.2 Macro Processor Algorithm and Data Structures
To solve the problem is Fig. 4.3, our DEFINE procedure maintains a counter named LEVEL.
MACRO directive is read, the value of LEVEL is inc. by 1.
MEND directive is read, the value of LEVEL is dec. by 1.
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4.2 Machine-Independent Macro Processor Features 4.2.1 Concatenation of Macro Parameters
Most macro processors allow parameters to be concatenated with other character strings.
A program contains one series of variables named by the symbols XA1, XA2, XA3, …, another series named by XB1, XB2, XB3, …, etc.
The body of the macro definition might contain a statement like
SUM Macro &ID
LDA X&ID1
LDA X&ID2
LDA X&ID3
LDA X&IDS
4.2.1 Concatenation of Macro Parameters
The beginning of the macro parameter is identified by the starting symbol &; however, the end of the parameter is not marked.
The problem is that the end of the parameter is not marked. Thus X&ID1 may mean “X” + ID + “1” or “X” + ID1.
In which the parameter &ID is concatenated after the character string X and before the character string 1.
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4.2.1 Concatenation of Macro Parameters
Most macro processors deal with this problem by providing a special concatenation operator (Fig. 4.6).
In SIC or SIC/XE, -> is used
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4.2.2 Generation of Unique Labels
As we discussed in Section 4.1, it is in general not possible for the body of a macro instruction to contain labels of usual kind.
WRBUFF (line 135) is called twice.
Fig. 4.7 illustrates one techniques for generating unique labels within a macro expansion.
Labels used within the macro body begin with the special character $.
Each symbol beginning with $ has been modified by replacing $ with $AA.
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4.2.3 Conditional Macro Expansion
The use of one type of conditional macro expansion statement is illustrated in Fig. 4.8.
The definition of RDBUFF has two additional parameters: &EOR and &MAXLTH.
Macro processor directive SET
This SET statement assigns the value 1 to &EORCK.
The symbol &EORCK is a macro time variables, which can be used to store working values during the macro expansion. RDBUFF F3,BUF,RECL,04,2048 RDBUFF 0E,BUFFER,LENGTH,,80 RDBUFF F1,BUFF,RLENG,04
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4.2.3 Conditional Macro Expansion
A different type of conditional macro expansion statement is illustrated in Fig. 4.9.
There is a list (00, 03, 04) corresponding to &EOR.
%NITEMS is a macro processor function that returns as its value the number of members in an argument list.
%NITEMS(&EOR) is equal to 3.
&CTR is used to count the number of times the lines following the WHILE statement have been generated.
Thus on the first iteration the expression &EOR[&CTR] on line 65 has the value 00 = &EOR[1]; on the second iteration it has the value 03, and so on.
How to implement nesting WHILE structures?
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4.2.4 Keyword Macro Parameters
Positional parameters Parameters and arguments were associated with each other according to their positions in the macro prototype and the macro invocation statements.
A certain macro instruction GENER has 10 possible parameters.
GENER MACRO &1, &2, &type, …, &channel, &10
GENER , , DIRECT, , , , , , 3
4.2.4 Keyword Macro Parameters
Keyword parameters Each argument value is written with a keyword that names the corresponding parameter.
Arguments may appear in any order.
GENER , , DIRECT, , , , , , 3 GENER TYPE=DIRECT, CHANNEL=3 GENER CHANNEL=3, TYPE=DIRECT
parameter=argument
Fig. 4.10 shows a version of the RDBUFF using keyword.
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4.3 Macro Processor Design Options 4.3.1 Recursive Macro Expansion
In Fig. 4.3 we presented an example of the definition of one macro instruction by another.
Fig. 4.11(a) shows an example - Dealt with the invocation of one macro by another.
The purpose of RDCHAR Fig. 4.11(b) is to read one character from a specified device into register A, taking care of the necessary test-and-wait loop.
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4.3.1 Recursive Macro Expansion
Fig. 4.11(c), applied to the macro invocation statement RDBUFF BUFFER, LENGTH, F1
The procedure EXPAND would be called when the macro was recognized.
The arguments from the macro invocation would be entered into ARGTAB as follows:
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4.3.1 Recursive Macro Expansion
The Boolean variable EXPANDING would be set to TRUE, and expansion of the macro invocation statement would be begin.
The processing would proceed normally until line 50, which contains a statement invoking RDCHAR. At that point, PROCESSLINE would call EXPAND again.
This time, ARGTAB would look like
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4.3.1 Recursive Macro Expansion
At the end of this expansion, however, a problem would appear. When the end of the definition of RDCHAR was recognized, EXPANDING would be set to FALSE.
Thus the macro processor would “forget” that it had been in middle of expanding a macro when it encountered the RDCHAR statement.
Use a Stack to save ARGTAB.
Use a counter to identify the expansion.
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4.1 Basic Macro Processor Functions4.1.1 Macro Definition and Expansion
4.1.2 Macro Processor Algorithm and Data Structures
4.1.2 Macro Processor Algorithm and Data Structures
4.1.2 Macro Processor Algorithm and Data Structures
4.1.2 Macro Processor Algorithm and Data Structures
4.1.2 Macro Processor Algorithm and Data Structures
4.1.2 Macro Processor Algorithm and Data Structures
4.2 Machine-Independent Macro Processor Features 4.2.1 Concatenation of Macro Parameters
4.2.1 Concatenation of Macro Parameters
4.2.1 Concatenation of Macro Parameters
4.2.2 Generation of Unique Labels
4.2.2 Generation of Unique Labels
4.2.2 Generation of Unique Labels
4.2.3 Conditional Macro Expansion
4.2.3 Conditional Macro Expansion
4.2.4 Keyword Macro Parameters
4.2.4 Keyword Macro Parameters
4.3.1 Recursive Macro Expansion
4.3.1 Recursive Macro Expansion
4.3.1 Recursive Macro Expansion